Ice Stone???

[Ullion]

I'm pretty sure it will utilize the same ice-rock location that Eevee will end up needing to use if someone wants a Glaceon in Alola. And we already know (from the Alolan forms of vulpix/ninetales/sandshrew/sandslash trailers) that there is a snowy location where we can catch them. So it seems reasonable that we would evolve them there as well.